Trunnion liner assembly for rotary grinding mill or the like

ABSTRACT

In a rotary grinding mill or the like the inlet and discharge trunnions of the mill are respectively provided with a liner assembly comprising a radially outer or primary liner and a radially inner or secondary liner. The primary liner normally remains permanently installed and is provided with a pair of axially spaced tract slots of T-shaped cross section. The secondary liner is adapted for easy installation or removal and is secured to the primary liner by boltlike fastening means which are received in the T-shaped track slots of the primary liner. Each track slot is provided with an access opening which permits initial engagement of the fastening means with the track slot. Instead of using a primary liner having track slots therein, the track slots may be formed directly in the trunnion, and the liner is secured by fasteners to the track slots of the trunnion.

United States Patent 3,318,537 5/1967 Wallinetal 72] Inventor Raymond C. Jenness 241/183 Milwaukee, Wis. 3,401,893 9/1968 Reynolds 241/179 X [21] 1 970 Primary Examiner-Granville Y. Custer, Jr. [22] I 8 AttorneysRobert C. Sullivan, Robert B. Benson and Arthur [45] Patented Sept. 14, 1971 M Streich [73] Assignee Allis-Chalmers Manufacturing Company Milwaukee, Wis. I 7 v v 7 ABSTRACT: In a rotary grinding mill or the like the inlet and [54] TRUNNION LINER ASSEMBLY FOR ROTARY discharge trunnions of the mill are respectively provided with GRINDING MILL OR THE LIKE a liner assembly comprising a rad ally outer or primary liner 14 Claims 6 Drawing Figs and a radially Inner or secondary liner. The primary 1mer normally remains permanently installed and 15 provided with a [52] US. Cl 241/182, pair f axially Spaced "act 1 f T Shaped cross Section The 241/300 secondary liner is adapted for easy installation or removal and [51] lnLCl 1302c 17/22 is Secured to the primary liner by bomike f t i means [50] Field of Search 241 179, which are received in the T shaped track slots f the primary 181, 182, 183, 284, 28 300 liner. Each track slot is provided with an access opening which permits initial engagement of the fastening means with the [56] References cued track slot. Instead of using a primary liner having track slots UNITED STATES PATENTS therein, the track slots may be formed directly in the trunnion, 1,018,320 2/1912 Holthoff 241/182 and the liner is secured by fasteners to the track slots of the 1,053,084 2/1913 Capen 241/182 trunnion.

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TRUNNION LINER ASSEMBLY FOR ROTARY GRINDING MILL OR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to rotary grinding mills or the like and more particularly to a liner assembly for a trunnion of a rotary grinding mill or the like.

2. Related Applications This application is related to and is an improvement on the subject matter of a U.S. Pat. application Ser. No. 15,566 of Richard E. Sabaski entitled Trunnion Liner Assembly for Rotary Grinding Mill or the Like, assigned to the same assignee as the present application, and filed in the. United States Patent Office on Mar. 2, 1970.

3. Description of the Prior Art Large grinding mills of the type utilized for grinding ore, cement, or the like such as ball mills, rod mills or mills of the autogenous type, are all conventionally provided with inlet and discharge trunnions at the feed end and discharge end, respectively of the rotary grinding mill. It is conventional to provide such inlet and discharge trunnions respectively with a liner formed of a hard wearing material, such as a suitable steel alloy, to protect the softer material of the trunnion itself, such as cast iron or the like, from the abrasive wear of the material being processed.

It is also known in the art to provide a liner for the liner. For clarity in description in the specification and claims which follow, the radially outer liner which is secured to the trunnion will be referred to as the primary liner while the linerliner which is secured to and lies radially inwardly of the primary liner will be referred to as the secondary liner." It will be understood, of course, that when the primary liner is lined with a secondary liner the material being processed when passing through the trunnion contacts only the surface of the secondary liner and hence the secondary liner must be constructed of a material having a good wear characteristic, such as a suitable alloy steel.

As previously mentioned, while it has been known to use inner or secondary liners in conjunction with outer or primary liners for lining the trunnions of grinding mills or the like, several types of arrangements heretofore used for mounting a secondary liner onto a primary liner of which I am aware have proved unsatisfactory. For example, in one such prior art arrangement for securing an inner or secondary liner to an outer or primary liner, a through slot large enough to receive the narrower dimension of the head of a T-bolt has been provided in the outer liner and a shank receiving passage has been provided in the inner liner. In such prior art arrangement the head end of the T-bolt is inserted in a radially outward direction through the slotlike passage of the outer liner, and the bolt is then turned so that the longer dimension of the head portion of the bolt is transverse of the through slot in the outer liner to prevent unintended return movement of the bolt. Such arrangement is commonly known in the art as a gun lock" type fastening and has the disadvantage that while it permits removal of the inner liner without removing the outer liner, it also permits leakage of the material being processed through the bolt-receiving passages just described into direct contact with the surface of the trunnion casting, thereby defeating the purpose of the trunnion liner arrangement. In another construction with which I am familiar for securing the inner liner to the outer liner, conventional bolting means are used for bolting the inner liner to the outer liner, which requires that the entire liner assembly including both the outer and inner liners be removed from the trunnion to permit replacement of the inner liner. The necessity of removing the entire liner assembly in order to replace the inner or secondary liner is inconvenient, particularly in the case of grinding mills having center type drives, since in center type drive mills, the drive coupling must be disconnected in order to remove the liner assembly in the second example just given.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a liner assembly for a trunnion of a rotary grinding mill or the like and the combination of such liner assembly with a rotary grinding mill or the like, having economic and operational advantages over the apparatus of the prior art.

It is another object of the invention to provide a liner assembly for the trunnion of a rotary grinding mill or the like, and the combination of such liner assembly with a rotary grinding mill or the like, which is characterized by ease of installation or of replacement, and requiring a minimum of down time of the mill.

It is another object of the invention to provide a liner assembly for the trunnion of a rotary grinding mill or the like and the combination of such liner assembly with a rotary grinding mill or the like which includes an outer or primary liner secured to the trunnion and an inner or secondary liner secured to the outer liner, so constructed as to provide simplicity and ease of assembly of the inner liner relative to the outer liner and so constructed as to permit easy replacement of the inner liner without the necessity of removing the outer liner from the trunnion.

It is a further object of a modified embodiment of the invention to provide a trunnion liner arrangement for a grinding mill or the like in which the trunnion is especially adapted to permit easy attachment or detachment of the liner relative to the trunnion.

In achievement of these objectives, there is provided in accordance with this invention a liner assembly for the trunnion of a rotary grinding mill or the like, and the combination of such a liner assembly with a rotary grinding mill or the like, comprising a radially outer or primary trunnion liner secured to the trunnion and a radially inner or secondary trunnion liner formed in arcuate segments which are secured to the primary liner by means of a boltlike fastener means which engage a T-shaped cross section track slot in the primary liner, the boltlike fastener means being initially engaged with the track slot through an access opening in the track slot. A further feature of the construction is the provision of a dam or barrier at a predetermined location in the track slot which serves to properly orient the segments of the secondary liner and also prevents circulation of processed material in the track slot. Instead of using a primary liner having track slots therein, the track slots may be formed directly in the trunnion, and the liner is secured by fasteners to the track slots of the trunnion.

Further objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in longitudinal section of a rotary grinding mill having a trunnion liner assembly in accordance with the invention;

FIG. 2 is an enlarged view in longitudinal section of a trunnion provided with the trunnion liner assembly of the invention;

FIG. 3 is an end view of the trunnion in FIGS. 1 and 2 showing the attachment of the trunnion liner assembly to the trunnion;

FIG. 4 is a partial view taken along line IV-IV of FIG. 3;

FIG. 5 is a partial view in section taken along line VV of FIG. 3; and

FIG. 6 is a view similar to FIG. 5 but showing an access opening of square cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and more particularly to FIG. I, there is shown a grinding mill generally indicated at 10 including a shell generally indicated at 12 comprising a cylindrical shell plate 14 to the respective opposite axial ends of which are rigidly attached shell flanges 16 and 16. Shell flanges 16 and 16' have ribs 18 rigidly secured thereto or integral therewith. Shell flange 16 is rigidly secured as by bolts 20 and nuts 21 to the end plate or head 22 which is integral with the trunnion 24 upon which the mill is supported for rotation by bearing 26. The shell flange 16' is similarly secured to the end plate or head 22' at the discharge end of the mill. The trunnion 24 at the left-hand end of the view of FIG. 1 is hollow and constitutes the feed end trunnion of the mill, and the trunnion 24 at the right-hand end of the view of FIG. 1 is hollow and serves as the discharge trunnion of the grinding mill.

The grinding mill is provided at the feed end thereof with a war plate and lifter assembly generally indicated at 30. At the discharge end of the mill, the mill is provided with a discharge diaphragm assembly generally indicated at 32 comprising a grate and wear plate subassembly 33 and a discharge casting subassembly 37 which cooperates with a discharge cone assembly generally indicated at 34 and with a ring liner 38 to define a discharge passage generally indicated at 36 through which the material after being ground passes outwardly to the discharge trunnion 34.

The feed trunnion 24 and the discharge trunnion 24' are each respectively provided with a liner assembly constructed in accordance with the invention. The trunnion liner assembly at the discharge end of the mill will be described in detail as exemplary of the trunnion liner assemblies which may be used at both the feed and discharge ends of the mill, while the trunnion liner assembly illustrated at the feed end of the mill shows a modified trunnion liner assembly which also may be used at either end of the mill.

Referring now to FIGS. 1, 2 and 3, the outer or primary liner generally indicated at 40 is seated inside the trunnion 24. The outer trunnion liner 40 in the illustrated embodiment is of fabricated construction and includes an axially inner ring portion 42 and an axially outer ring portion 44 which are joined by a connecting member 46. The connecting member 46 is welded at its axially inner end to ring member 42 and at its axially outer end to ring member 44.

The ring liner 38 projects radially inwardly beyond the radially inner peripheral surface of trunnion 24' and terminates flush with the radially inner surface of ring portion 42 of outer or primary trunnion liner 40. The axially inner surface of ring portion 42 of outer; or primary trunnion li-ner 40 is in abutting relation to the axially outer surface of ring liner 38. Ring portion 42 of outer trunnion liner 40 is provided with an annular recess 48 contiguous ring liner 38. Recess 48 receives rib portion 45 of the trunnion 24, and a suitable packing material 47 is also positioned in recess 48.

In accordance with an important aspect of the construction, the ring portions 42 and 44 of outer liner 40 are respectively provided with slotlike recesses or track slots each indicated at 49. Each of the track slots 49 extends for 360 of the periphery of the respective ring members 42 and 44. Each of the slotlike recesses or track slots 49 is of the T-shape in hollow cross section. Each track slot includes a radially outer head portion 51 and a radially inner neck portion 53. As will be explained in more detail hereinafter, head portion 51 of the track slot normally receives the head end of a fastening bolt while neck portion 53 of the track slot normally receives the shank portion of the fastening bolt.

The axially outermost ring member 44 is provided with a flange portion 50 which extends in a 360 arc and is suitably secured to the trunnion 24'. If the trunnion itself is provided with a cooperating flange portion as shown in the drawings, the flange portion 50 of the primary liner is bolted to the trunnion by bolts passing through both the flange 50 and through the cooperating flange of the trunnion. If the trunnion is not provided with a cooperating flange, then flange 50 of the primary liner 40 is bolted by tap bolts into the end face of the trunnion.

The radially inner or secondary liner generally indicated at 60 comprises a plurality of arcuate segments 61 indicated at 61a, 61b, 61c, 61d, 61e, and 61f, respectively, in the view of FIG. 3. In the illustrated embodiment, it is assumed that six arcuate segments 61 as just described are provided and that each segment spans an arc of 60 of the internal periphery of the trunnion. However, it will be understood that this is merely by way of example and a different number of segments could be used. The secondary liner segments 61 are formed of a material having good wear characteristics since it is the secondary .liner which absorbs the wear from the load of processed material passing through the trunnion. A typical material of Y which the secondary liner 60 might be constructed would be 0.85 percent carbon chrome-moly alloy steel. The secondary liner segments 61 when assembled into a 360 arc define a truncated conical form which is of larger diameter at the discharge or right-hand end of the view of FIG, 2 than at the left-hand of the view of FIG. 2.

Each of theliner segments 61 is provided adjacent the opposite ends thereof with a countersunk bolt hole such as that indicated at 62 in FIG. 2.

An important feature of the construction is the provision in each of the slot tracks 49 of a dam 64 (FIG. 3 and FIG. 5) at a predetermined location in each of the respective track slots. The dam 64 is an abutment and closure which extends across both head portion and neck portion of the track slot 49 and which serves the following dual functions:

I. it serves as an abutment means for the bolt 66 which secures the segment 61a in position and thus serves to orient the plurality of segments 61 at a predetermined location relative to the track slot 49 such that in the final assembled position of secondary liner 60 the bolt hole 62 for any given liner segment 61 is not aligned with the access opening 55 of the track slot 49 as will be described hereinafter.

2. dam 64 also serves to prevent racing of processed material which gets into track slot 49 since dam 64 serves as a barrier which prevents 360 rotation of processed material in track slot 49. It is inevitable that processed material will get into track slots 49 and will become packed therein. However, by stopping 360 rotation of such material in the track slots, abrasive wear on the track slots is prevented.

It will be noted that the abutting circumferential ends of contiguous segments such as 61a and 61b are preferably provided with a stepped configuration or overlap to prevent leakage of the processed material through the joint between adjacent segments of the secondary liner and into contact with the face of the primary trunnion liner 40. A suitable packing material 63 is preferably provided between the abutting edges of contiguous segments 61 at the joint thereof. While abutting circumferential ends of contiguous segments such as 610 and 61!; are preferably overlapped as just described, such abutting circumferential ends do not have to be so overlapped but may instead by butt jointed.

The slot track 49 on each primary trunnion liner 40 is provided at one point in its periphery with an access opening 55 (FIG. 4) or 55' (FIG. 6) which is so dimensioned as to receive the head end 68 of the bolt respectively generally indicated at 66 for holding the respective secondary liner segments in position. The access opening 55 may be alternatively of round cross section (as indicated at 55 in FIG. 5) or square cross section (as indicated at 55' in FIG. 6) and is of sufficient crosssectional dimension to permit the head end 68 of bolt 66 to be inserted into engagement with head portion 51 of track slot 49. The access opening 55 is in effect an enlarged region of neck portion 53 of track slot 49.

To assemble the secondary liner segments 61 relative to the primary liner 40, a first one of the secondary liner segments such as 61a is positioned in overlying position to the primary liner 40 and with a bolt 66 received in each of the respective passages 62 of the given liner segment and with the head end 68 of each bolt being aligned with the corresponding access opening 55 or 55 of primary trunnion liner 40. The head end 68 of bolt 66 on each end of the given secondary liner segment is inserted through a corresponding access opening 55 or 55' and into engagement with the track slot 49 at each end of the primary trunnion liner. When the bolt 66 is so positioned, the head end 68 of the bolt will be received in head portion 51 of track slot 49 and the shank portion of the bolt will lie in neck portion 53 of the track slot. The head end 68 of the bolt 66 may be of square or of hexagonal shape and the head end 68 is dimensionally related to the head portion 51 of slot track 49 in such manner that rotation of bolt 66 is prevented. The first secondary liner segment to be so installed is then moved to a position in which its oppositely disposed bolts 66 abut against the respective dams 64 in each of the respective track slots 49. After the first secondary liner segment such as 61a has been positioned as just described, the remaining segments 61 are then placed into position with the bolts of each respective seg ment 61 first engaging the access openings 55 or 55' of the respective track slots 49, the respective secondary liner segments being then moved to proper position, as seen in FIG. 3, with the respective bolts 66 of the respective segments 61 moving along the track slots 49 as the respective segments 61 are moved to their proper position relative to the remaining segments and relative to the primary liner 40. in the final assembled position of the segments 61, the abutting end edges of contiguous segments 61 overlap as shown in FIG. 3. After the respective segments 61 have been positioned in assembled relation as shown in the view of FIG. 3, the nuts 70 which secure the respective secondary liner segments 61 tightly in position are tightened onto the threaded shank portion of the respective bolts 66, the nuts 70 being received in countersunk openings 62 in the radially inner face of the respective secondary liner segments.

it can be seen that it it is necessary to remove the secondary liner 60 as, for example, for the purpose of replacing a worn secondary liner with a new secondary liner, that the reverse procedure to that just described is followed.

It can be seen from the foregoing that there is provided in accordance with this invention an improved liner assembly for the trunnion of a grinding mill or the like which permits quick and easy installation of the secondary trunnion liner onto a primary trunnion liner, the primary liner remaining a permanent installation insofar as normal operation of the grinding mill is concerned. Furthermore, the construction hereinbefore described permits quick and easy removal of an existing secondary liner for purposes of replacement or the like without removal of the primary liner thereby saving a great deal of down time" of the grinding mill or the like. The mounting arrangement of the secondary liner on the primary liner is such that no leakage occurs of the processed material onto the surface of the trunnion. A further advantage of the subject construction is that on center-type drives for grinding mills or the like, the coupling never has to be broken to remove a worn secondary trunnion liner of the type hereinbefore described since removal of the secondary trunnion liner hereinbefore described does not require removal of the primary trunnion liner, the removal of which would require uncoupling of the center-type drive.

It is also within the scope of this invention to provide slot- 1 like recesses such as T-shaped cross section slot tracks 49a similar to the previously described track slots 49 directly in the trunnion, as embodied in the trunnion portion 24a of the head trunnion 24 at the left-hand end of the view of FIG. 1, rather than in a primary lining, to provide each such track slot with an access opening similar to the access opening or 55 previously described, and to mount segmented liner members a directly onto the trunnion portion 24a by means of fasteners similar to the previously described fasteners 66 which are secured in the track slots 49a. Each track slot 49a is also provided with a dam such as the dam 64, previously described.

It will be understood that the modified embodiment just described in which the track slots 49a are provided directly in the trunnion is similar in principle to the previously described embodiment in which the track slots 49 are provided in a primary liner 40 which is secured in the trunnion 24', and that the segmented liner members 60a are secured to the track slots 49a on trunnion portion 24a in substantially the same manner as described in connection with the mounting of the secondary liner segments 61 relative to primary liner 40.

Either construction, namely, that shown at the feed end or that shown at the discharge end, may be used at either end of the grinding mill or the like.

From the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been obtained in a preferred manner. However, modifications and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A rotary grinding mill or the like comprising a trunnion, a track slot positioned within and carried by said trunnion and extending through an arc of substantially 360 relative to said trunnion, said track slot being of substantially. T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a liner carried by said trunnion, fastener means extending through said liner and received in said track slot, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastener means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.

2. A rotary grinding mill or the like as defined in claim 1 in which said liner is formed of a hard material having good wear characteristics.

3. A rotary grinding mill as defined in claim 1 in which said liner is formed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.

4. A rotary grinding mill or the like as defined in claim I in which said track slot is provided with a dam at one region thereof.

5. A rotary grinding mill or the like as defined in claim 3 in which adjacent ends of contiguous arcuate segments are overlapped.

6. A rotary grinding mill or the like comprising a trunnion, a primary liner secured to said trunnion, a track slot carried by said primary liner, said track slot extending through an arc of substantially 360 relative to said trunnion, said track slot being of substantially T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a secondary liner positioned in superposed relation to said primary liner radially inwardly of said primary liner, fastener means extending through said secondary liner and received in said track slot of said primary liner whereby to secure said secondary liner to said primary liner, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastener means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.

7. A rotary grinding mill or the like as defined in claim 6 in which said secondary liner is formed of a hard material having good wear characteristics.

8. A rotary. grinding mill or the like as defined in claim 6 in which said secondary liner is formed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.

9. A rotary grinding mill or the like as defined in claim 8 in which adjacent ends of contiguous arcuate segments are overlapped.

10. A trunnion liner assembly adapted to be mounted in the trunnion of a rotary grinding mill or the like comprising a primary liner adapted to be secured to said trunnion, a track slot carried by said primary liner, said track slot extending through an arc of substantially 360 relative to said trunnion, said track slot being of substantially T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a secondary liner positioned in superposed relation to said primary liner radially inwardly of said primary liner, fastener means extending through said secondary liner and received in said track slot of said primary liner whereby to secure said secondary liner to said primary liner, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastener means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.

11. A trunnion liner assembly as defined in claim 10 in which said secondary liner is formed of a hard material having good wear characteristics.

12. A trunnion liner assembly as defined in claim 10 in which said secondary liner isformed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.

13. A trunnion liner assembly as defined in claim 10 in which said track slot is provided with a dam at one region thereof.

14. A trunnion liner assembly as defined in claim 10 in which adjacent ends of contiguous arcuate segments are overlapped. 

1. A rotary grinding mill or the like comprising a trunnion, a track slot positioned within and carried by said trunnion and extending through an arc of substantially 360* relative to said trunnion, said track slot being of substantially T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a liner carried by said trunnion, fastener means extending through said liner and received in said track slot, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastEner means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.
 2. A rotary grinding mill or the like as defined in claim 1 in which said liner is formed of a hard material having good wear characteristics.
 3. A rotary grinding mill as defined in claim 1 in which said liner is formed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.
 4. A rotary grinding mill or the like as defined in claim 1 in which said track slot is provided with a dam at one region thereof.
 5. A rotary grinding mill or the like as defined in claim 3 in which adjacent ends of contiguous arcuate segments are overlapped.
 6. A rotary grinding mill or the like comprising a trunnion, a primary liner secured to said trunnion, a track slot carried by said primary liner, said track slot extending through an arc of substantially 360* relative to said trunnion, said track slot being of substantially T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a secondary liner positioned in superposed relation to said primary liner radially inwardly of said primary liner, fastener means extending through said secondary liner and received in said track slot of said primary liner whereby to secure said secondary liner to said primary liner, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastener means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.
 7. A rotary grinding mill or the like as defined in claim 6 in which said secondary liner is formed of a hard material having good wear characteristics.
 8. A rotary grinding mill or the like as defined in claim 6 in which said secondary liner is formed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.
 9. A rotary grinding mill or the like as defined in claim 8 in which adjacent ends of contiguous arcuate segments are overlapped.
 10. A trunnion liner assembly adapted to be mounted in the trunnion of a rotary grinding mill or the like comprising a primary liner adapted to be secured to said trunnion, a track slot carried by said primary liner, said track slot extending through an arc of substantially 360* relative to said trunnion, said track slot being of substantially T-shape in transverse cross section and including a radially outer head portion and a radially inner neck portion, a secondary liner positioned in superposed relation to said primary liner radially inwardly of said primary liner, fastener means extending through said secondary liner and received in said track slot of said primary liner whereby to secure said secondary liner to said primary liner, said fastener means including a head end and a shank, said head portion of said track slot normally receiving the head end of said fastener means, said neck portion of said track slot normally receiving the shank of said fastener means and being of insufficient dimension along most of its length to permit passage therethrough of said head end of said Fastener means, said track slot including said neck portion thereof being enlarged at at least one location therealong to provide an access opening adapted to permit passage therethrough of said head end of said fastener means into engagement with said head portion of said track slot.
 11. A trunnion liner assembly as defined in claim 10 in which said secondary liner is formed of a hard material having good wear characteristics.
 12. A trunnion liner assembly as defined in claim 10 in which said secondary liner is formed of a plurality of arcuate segments, each of said segments being secured by fastener means to said track slot.
 13. A trunnion liner assembly as defined in claim 10 in which said track slot is provided with a dam at one region thereof.
 14. A trunnion liner assembly as defined in claim 10 in which adjacent ends of contiguous arcuate segments are overlapped. 